Compute a file HMAC with a secret key (SHA-256/1/384/512 or MD5) - fully local in your browser; the file and key never leave your device.
Running locally on your device ...
Running locally on your device ...
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Your files never left your device
No. Everything runs in your browser - your file never leaves your device. How this is verifiable
An HMAC (keyed-hash message authentication code, RFC 2104 / FIPS 198-1) is a checksum with a key: unlike a plain hash it proves not only that a file is unchanged, but also that it comes from someone who knows the same secret key. Only a holder of the key can reproduce the same value - which makes an HMAC suitable for confirming the authenticity and integrity of a file between two parties who agreed on a key beforehand.
You pick the underlying hash function. SHA-256 is today’s standard and the right choice when nothing else is required. SHA-384 and SHA-512 give longer values from the same family; SHA-1 and MD5 are considered outdated and should only be used to match older systems. The key is entered as text and used as UTF-8 bytes - exactly like the command-line tools, so the result compares 1:1 with the value from openssl.
The computation runs entirely locally in your browser via the native Web Crypto interface - nothing is uploaded, nothing is stored, and no foreign library is loaded from a CDN. That matters especially for an HMAC: both the file and the secret key stay on your device. The result appears as a text file in the format hex value followed by the file name, directly comparable with a value produced elsewhere.
| Output format | TXT |
|---|---|
| Batch processing | Yes |
| Processing | Locally in your browser (JavaScript) |
| File upload | None |
Limitations: An HMAC ensures authenticity and integrity but does not encrypt anything - the file content stays readable. Its security rests entirely on the key: it must stay secret and be agreed over a secure channel. SHA-1 and MD5 are only meant for matching legacy systems, not for new security requirements.
| Algorithm | Output length | Status | Typical use |
|---|---|---|---|
| SHA-256 | 256 bits | Today's standard | general authenticity check |
| SHA-384 | 384 bits | Longer SHA-2 variant | where a longer signature is required |
| SHA-512 | 512 bits | Longer SHA-2 variant | where a longer signature is required |
| SHA-1 | 160 bits | Outdated | matching older systems only |
| MD5 | 128 bits | Outdated | matching older systems only |
No. Both stay local in the browser; the file and key never leave your device and are not stored.
A checksum only proves a file is unchanged. An HMAC additionally needs a secret key and thus also proves origin - only someone who knows the key can produce the value.
When in doubt, SHA-256. SHA-384 or SHA-512 for longer values, SHA-1 or MD5 only to match older systems.
Yes. The output is in the same format as the command line and matches the hex value of openssl dgst with the -hmac option and the chosen method.
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